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Finding the Fourth Proportional to 128.78, 177.78 and 85.19

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Solution

The fourth proportional to 128.78, 177.78 and 85.19 is: 117.60

Step by Step Solution

  1. Step 1: Write the proportion equation
    128.78 : 177.78 = 85.19 : x
  2. Step 2: Convert to fraction form
    128.78/177.78 = 85.19/x
  3. Step 3: Cross multiply
    128.78x = 177.78 × 85.19
  4. Step 4: Simplify right side
    128.78x = 15,144.19
  5. Step 5: Solve for x
    x = 15,144.19/128.78
  6. Step 6: Final answer
    x = 117.60

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Why These Related Problems?

These problems maintain the same ratio (1.38) or explore similar proportional relationships. Practicing with related ratios helps build understanding of proportional relationships.